Preliminary Studies on Rare Elements Addition and Effect on Oxidation Behaviour of Pack Cementation Coatings Deposited on Variety of Steels at High Temperature

Tomasz Dudziak,Ewa Rząd,Michal Wójcicki,Adelajda Polkowska,Katrin Jahns,Wojciech Polkowski,Tomasz Polczyk

doi:10.3390/ma14226801

Abstract

The aim of the paper was to investigate the air oxidation behaviour of pack aluminised steels exposed at 650 °C for 1000 h in static natural air atmosphere. The pack coatings were doped by rare elements such as gadolinium (Gd), cerium oxide (CeO2), and lanthanum (La) in order to enhance the corrosion resistance and plasticity of the deposited layers. In this work, the following steels were used: 16M, T91, VM12, Super 304H, and finally SANICRO25. The results indicated a much higher corrosion resistance in the coated 16M, T91, and VM12 steels; the steels with a higher Cr content than 16 wt % Cr indicated a better behaviour in the uncoated state than in the coated state. However, the observed difference in mass gain between the uncoated and the coated austenitic steels was not enormous. Furthermore, the addition of RE elements to the coating showed some effect in terms of coating thicknesses and differences in the layer structures. The materials prior to testing and after the exposure were investigated using XRD, the SEM X-ray maps with an EDS instrument were used for particular samples to evaluate the phase identifications, element concentrations, microstructure, and chemical composition.

Highlights

There are many different steel grades used in the power plant industry to secure energy production
In order to overcome the problem of the reduced oxidation resistance of low alloyed steels at high temperatures, diffusion coatings produced by pack cementation are an idea to develop new systems for the high-temperature protection of boiler steels
The presented X-ray mapping of the SANICRO25 steel coated by pack cementation coatings with the addition of La and addition of CeO2 are shown in Figures 18 and 19 respectively

Summary

Introduction

There are many different steel grades used in the power plant industry to secure energy production. Steels with remarkable mechanical properties and high-temperature oxidation resistance must be installed, while in the other sections where much lower temperatures are met (up to 500–550 ◦ C), the steels with up to 10 wt % Cr such as 16Mo3, T22, T91, and VM12 may be found. There are several steels with adequate oxidation resistance such as 304H or 316L to be used in the hottest sections of a power plant. In order to overcome the problem of the reduced oxidation resistance of low alloyed steels at high temperatures, diffusion coatings produced by pack cementation are an idea to develop new systems for the high-temperature protection of boiler steels. Further development toward the reduction of brittle phase formation concentrated around the transformation of

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Conclusion